Method of protecting concrete surfaces during curing



t No Drawing.

Patented Feb. 2 8, 1933 7 TBS UNITED sTA PAUL c. LEMMERMAN, on EAST cnnvnzcann, Ami RAYMOND IE. nEML-nR, or LAKEWOOD, onro, nssrenons TO THE GRASSELLI CHEMICAL coMPANxor CLEVELAND, omo,

t A. CORPORATION OF DELAWARE nn'rnon or rnomncrrmecoucnnrn sURrAoEs DURING cunmo' The strength and quality ofconcrete, such as used inhighways and floor construction, depend onanumber of factors, among which is the proper protection during the early setting, or curing, of the concrete by a covering which will' prevent fexcessive evaporation and loss of the water contained in the cement mixture as laid. I

One of the common methods used for this protection is to cover the surface with a layer of earth or straw which is continuously kept moist by sprinkling with water; This is a rather cumbersome'and expensive procedure, and it has extensively been replacedby applying to the freshlyflaid concrete surface various chemicals or their solutions. Some of these chemicals prevent excessive evaporation of the water contained in the fresh concrete by sealing the surface; others, due to their hygroscopic nature, attract moisture "to the surface of the concrete. v g 7 Sodium silicate solutions are extensively used for this purpose. Such solutions are applied in concentrations up to a densityof a out 36 Be, and the grade ofsodiumsili- 'cate preferred has a ratio of Na O to SiO of q about 1 to not less than 3.2 by weight. The application of sodium silicate to concrete during the curing period usually comprises protecting the surface with wet burlap for the first 24 hours, after which a sodium silicate solution of theabove-concentration is brushed upon the concrete, where, upon drying it seals the pores of the surface and thereby reduces the evaporation of the miXing water during the curingperiod.

We have found that the quality of the seal produced by the slow evaporation of a sodium silicate-solution brushed upon concrete surfaces is. improved if the solutions con- ;tains, besides caustic alkali and s1l1c1c acid,

small amounts of another electrolyte, and

"our invention comprises protecting concrete surfaces during curing by applying thereto a solution of sodium silicate containing small amounts of'an electrolyte; j It is, for the understanding of the present invention,unnecessary to assume or discuss any of thevarioustheories relating to the a composition of the various'ingredients precipitating amounts of non-caustic elec- 1 Application filed November 13', 1930. serial no; 495,418.:

make up sodium silicate solutions. It suffices to know that the addition to sodium silicate solutions of substantial amounts of noncaustic electrolytes,'that is to say: those which are salts oracids in aqueous solution, precipitates silicic acid.

Sodium silicate solutions will, however, tolerate small amounts of such precipitating electrolytes without precipitating silicic acid and our inventioncontemplates the use of sodium silicate solutions containing non causticelectrolytes 1n amountsinsufficient to precipitate silicic acidfrom the solution. a

The amounts of non-caustic electrolytes which can be added to sodium silicate solusolution andwwith thesnature of the electrolyte. While,-for'instance, 8% of a'36% hy drochloric acid will precipitate, or cause to settle out, silicicvacid from a 33% B.v solui 95' tions without preclpitatmg siliclc acid vary with the composition, concentration ofthe tion of a 1 :32 ratio, 1% will not do so, simi- .larly, concentrate sulfuric acid will not prec1p1tate,While 4% will do so atroom tem- I 'pera re. i

(20 to 30 C.) a 'Additions to: sodium silicate which do not cause silicic acid to' settle out of solution will hereinafter be termednon-precipitating withoutany implications as to the chemical reactions. which may takeflp'lace between the electrolyte and the ingredientsofthe silicate solution.f r

Sodium silicate solutions containing nontrolyt'es were found by us when I applied to uncured concrete, to seal the pores of the con- ;crete infless time than straight sodium silicate solutionsapplied under the same coneditions. f

we also found that theso obtained seals were less pervious to water vapor and that concrete-surfaces protected by such seals durbya' seal obtained fromstraight sodium silicate. 7

1 ing curing lost less oftheir water by evapo ra- 7 'tion in afgiven time than surfaces protected .95 w a The concrete surfaces" cured while protecttoo showed no detrimental effect from the action the ratio lNa O to 3.2 SiO (by weight) and found that nosilicic acid settled out of the solution under ordinary conditions. These solutions, when spread on green concrete, set in one-fifth to two-thirds of the time required for straight sodium silicate solutions of the same gravity and produced seals on the concrete surfaces which efliciently protected said surfaces during curing:

WY: Percent Glacial acetic, acid -i 1% Glacial acetic acid with the addition of -from to 2% glycerine 1, Y OXalic acid crystals 1 Formic acid, 90% 1 Benzoic aci d Sodium acetate crystals 4 i Sodium benzene sulfonate Q 1 Sodium alginate 4 Phenol 1 V Crude calcium ligninf.sulfonate' 2 Hydrochloric acid, 36% 2 Concentrated phosphoric acid 1 Concentrated sulfuricacid 1 1 :Sodium nitrate 4 Sodium chloride 4. Tri-sodium phosphate .hydrate 3 Calcium chloride Aluminum chloride crystals,-and others i" The, amountsj'stated are basedvupon the weight of the sodium silicate solution. They do not necessarily represent maxlmum amounts tolerated by the sodiumsilicate and on the other hand, smaller amountshave produced similarefiects.

" We also found that among the non-caustic electrolytes added in non precipitating amounts to sodium silicate s0lut1ons,"weak' acids, particularly weak organic acids, were among the most eflicient in protecting the uncured concrete.

1 One may consider that the addition of said lweak acids, to sodium silicate solutions changes the Na O toSiO ratio. We do not believe, however, that such a change is the main factor determining the improved quality of the seal produced. On the one hand, a

sodium silicate solution of a ratio corresponding to such possible'change does not show the improvement; on the other hand, the, add

tion of alkali-metal salts or other water'soluble salts of thesame acids, where there will be no change of ratio, produces substant ally the most desirable electrolytes to be added tosodium silicate solutions for use in proproperties by the addition of acid thereto,

app o i y be required.

tecting concrete surfaces during the curing period.

It is, of course, understood that acids, such as acetic acid, etc., added toa sodium silicate solution do not appear in the solution as free acids, and when we speak herein of sodium silicate solutions containing acid we are merely conveyingthe idea that the sodium silicate solution has been modified inits seal forming and that the solution contains the reaction product, whatever'that is, produced by said addition.

' It is rather diflicult to estimate qu'antita tivelythe improvements obtained by various treatmentsin situ of concrete surfaces during curing. Various laboratory methods" are known which dealwith themoisture retention during curing, flexural and. compressive straight sodium silicate solution.

The preparation of our modified sodium silicatesolutions is easily effected by adding the requisite amount of acetic acid or other non-caustic electrolyte to a concentrated sodium silicate solution. It is advisable to efliciently stirthe solution, as otherwise local high concentration of the electrolyte may precipitate silicic acid, though in most instances curds which precipitate will easily 'redissolve on continued agitation. The viscosity-of thev modified silicate solutions may be .difierent from that of the original solutions, but as such concentrated solutions are usually diluted to some degree, for instance to 33 or 36 B .,'.f0r spreading upon concrete surfaces, the'desired viscosity can easily be obtained. 7

" The modified solutions are appliedto concrete surfaces in" exactly the same mannerias ordinary silicate solutions. The solution is,

for instance, flushed onthe surface with a T 5 square yard, or by any other convenient method as well known in thisf'art. It isnot-neces- 1 g sary to use sodium silicate solutions 'of exactly 36-B. for application-to curing concrete roads; Similarly, we can use more concentrated modified solutions or dilute our silicate, containing electrolytes according to our invention, to a lesser-gravityfsuch as 25, 20 or even as low as 10 B., and obtaina good protection of concrete surfacesduring curing, though with dilute solutions, more than one We claimf 1. The method of protecting a concrete surface during curing which comprises applying to said surface a sodium silicate solution containing a non-precipitating amount of a non-caustic electrolyte.

2. The method of protecting a concrete surface during curing which comprises applying to said surface a sodium silicate solution containing a weak organic acid in an amount insuflicient to precipitate silicic acid from said solution.

3. The method of protecting a concrete surface during curing which comprises applying to said surface a sodium silicate solution containing a smallamount of acetic acid.

4. The method of protecting a concrete surface during curing which comprises applying to said surface a sodium silicate solution containing an amount of sodium acetate insufficient to precipitate silicic acid from said solution.

5. The method of protecting a concrete surface during curing which comprises applying to said surface a sodium silicate solu-- tion containing an amount of a water soluble salt insuiiicient to precipitate silicic acid from said solution.

6. The method of protecting a concrete surface during curing which comprises forming a seal for the pores of said surface by apply- 7 ing thereto, before completion of the cure, a sodium silicate solution containing a nonprecipitating amount of a non-caustic elec trolyte.

In testimony whereof, we afiix our signatures. 1

PAUL C. LEMMERMAN; RAYMOND F. REMLER. 

